The present disclosure relates to an image sensor and a method of manufacturing the same. More specifically, the present disclosure relates to a complementary metal oxide semiconductor (CMOS) image sensor having a reduced noise and a method of manufacturing the same.
In general, an image sensor is a semiconductor device that converts an optical image into electrical signals, and may be classified or categorized as a charge coupled device (CCD) or a CMOS image sensor (CIS).
The CMOS image sensor includes unit pixels, each including a photodiode and MOS transistors. The CMOS image sensor sequentially detects the electrical signals of the unit pixels using a switching method, thereby forming an image.
The CMOS image sensor may include photodiodes formed in a substrate, transistors formed on the substrate, wiring layers electrically connected with the transistors, and a color filter layer and micro lens array formed on the wiring layers.
Particularly, the CMOS image sensor may include pixel regions arranged in rows and columns, and each of the pixel regions may include a photodiode and a plurality of transistors electrically connected with the photodiode. For example, each pixel region may include a transfer transistor, a reset transistor, a source follower transistor and a select transistor electrically connected with the photodiode. Further, the CMOS image sensor may include a programmable gain amplifier (PGA), a correlated double sampling (CDS) circuit and an analog digital converter (ADC) in order to convert analog signals output from the pixel regions into digital signals.
Often, when defects such as dangling bonds are formed in a gate insulating layer of the source follower transistor connected with a floating diffusion region of the pixel region, the dangling bonds may function as electron trap sites, and thus temporal noise such as flicker noise (1/f Noise) may be generated. Further, when the dangling bonds are formed in gate insulating layers of amplifying transistors of the PGA and/or CDS circuit, flickering column noise may be generated.